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Gas mileage is affected by more than just the size and weight of the tire. Rolling resistance of the tire has a larger effect. Here’s the basic rule:

Harder tires = lower rolling resistance

Beware. If the tire is too hard or too round, then the tire-patch (which is the area of tire that is in contact with the ground) will be too small to grip the road surface effectively. This in turn will allow the wheel to skid easier when trying to stop or allow the wheel to slip and spin when trying to roll out from a light.

The same holds true for tread designs and patterns. The more detailed the tread design, the more likely it will grip the road better—but also create the opportunity to trap air in each of the pockets it generates when touching the road surface. When trapping the air/water/dirt/snow in these pockets, the tire is compressing the material that is in the pocket. Therefore, the engine has to do more work to compress these pockets. This makes the tire less efficient to turn, and thereby reduces the mileage of the vehicle.

The tire companies work to balance the rubber compounds and tread patterns to find the most efficient combinations. Along the way, new compounds are discovered as well as more efficient tread patterns.

Hybrids and Resistance

Most of the hybrid vehicles use some sort of low rolling resistance tire. Sometimes these tires are called “low mu.” “Mu” is the Greek letter (used by engineers) as the symbol for “tire friction to the road surface.”

While the low resistance tires will help with mileage, there have been some complaints from hybrid owners that they did not like the way the tires handle on the road. As a result, Toyota has backed off from using the lower resistance tires and has settled with a better handling tire.

It boils down to personal preference. If you drive aggressively, you might want to use a softer tire with better road adhesion. If you’re a fanatic for mileage and a very mellow driver, then you probably should get the lowest resistance tire you can find on the market.

Choice of Tire and/or Tire Pressure

You can minimize resistance, and maximizing mpg by making sure your car uses a Low Rolling Resistance (LRR) rated tire. If you change your vehicle’s tires, by increasing or decreasing the resistance by 20% for example, you may raise or drop mileage by 3 to 5%. While this is a measurable difference, it won’t make as big a difference as making certain that your tires are properly inflated. A vehicle that requires its tires to be inflated to 35 psi will have an increase in rolling resistance of 12% or more if the tires are allowed to become underinflated to just 28 psi.

Many hybrid car enthusiasts recommend an absolute minimum psi of 35 psi—and many try to push the envelope by increasing pressure to 40+ psi. You should read the manufacturer’s recommendations, and decide for yourself how comfortable you are with pumping up your tires for a gain in mpg. There could be safety issues related to over-inflating your tires.

Bear in mind that temperature makes a difference. The rule of thumb is for every 10° Fahrenheit change in air temperature, your tire’s inflation pressure will change by about 1 psi (up with higher temperatures and down with lower). When it gets cold, check your pressure to make sure it’s not too low.

This interview series about the future of the car is produced in collaboration with Auto FutureTech – Summit

R.A.D.O.A.E

In defense of those who like increasing tire pressure, there are a few things to consider. First, the prius is a fairly heavy car, weighing in at nearly 3000 pounds. Second. the 185 mm tire is not a very wide tire for distributing this weight. I have seen pressure recommendations similar on cars of the same weight, but riding on the larger 205 mm tires. to maintain the aspect ratio of the contact patch, a narrower tire placed on the same car needs considerably more inflation pressure to maintain the same tread surface deformation.
Another thing is that the prius is front heavy. front wheel drive cars usually are. the 23 lb chassis battery and the 119 Lb
nickel hydride battery only amount to the weight of a small person sitting in the back seat. up front, you have mg1, mg2, the power splitting device, and the combustion engine, along with the differential assembly, and finally, the driver, and perhaps a passenger putting their weight mostly on the front tires. so there is no problem upping the inflation pressure on the front tires, but be careful not to over-inflate the rear tires. The rear axle of the prius is solid. it’s a pseudo-trailing suspension. this is the type of suspension that has a tendancy to lift the inside rear tire right off the ground durring a hard corner. you will notice that the rear tires require less inflation pressure then the front. Look at this as a percentage, not an offset. if you plan to increase the front tires to 42 psi, stay between 38 and 39 psi on the rear. if you get too much pressure in the rear, the back end could skitter on a rough road. the tires will be too round, and will not keep enough rubber on the road for good handling or good tire life. this also puts undue stress on the axle and suspension components. It also flags the vehicle stability control when braking. the higher the pressure, the more noticeable the electronic traction control issue will be on rough road surfaces.

blue monkey

My Volkswagen Jetta TDI (Turbo Direct Injection Diesel), stick shift makes 40mpg average.
Of course i inflate tires conform the placard recommendation, but try the same thing in another car and hope you will get 40mpg??
PS.
I don’t need to replace a battery package $5000 – $7000 somewhere between 5 – 7 years.
If you use a Hybrid mostly in Electric mode, the battery pack dies in 3 to 5 years.

Tom

R.A.D.O.A.E made a very good post, IMO. I found all he says about high pressure in the rear of the car to be true dependent on tire choice at PROPER pressure- my old Goodyear Integrity (original factory equipment) skittered and skidded, NEW and used, but not as much my slightly lower mileage Kumho Solus KR21s. There was one particular highway ramp where my automatic traction control ALWAYS engaged with my old tires, and so far never has with the Kumhos. I also used to experience more “skittering” loss of braking on bumpy roads. Very disconcerting. Much less so now.

soalr perth

Very interesting I’m going to check the tyre pressure on my FWD car in the morning!!!

Mustang

To blue monkey, First off, we’re talking about hybrid cars, and using low rolling resistance tires or not.

Secondly, no one said you’d get 40 mpg just by inflating your tires to a higher psi.

Third, you’re obviously happy with your car, but if you think you get better mileage than a Prius, which lists at the same price as a tdi six speed, then you need to do a little research.

Just to keep things in perspective, since every one drives differently, lets use epa numbers. Prius city mpg = 50. Jetta tdi = 30.

Prius highway = 48, jetta = 41. Combined mpg Prius = 50, Jetta = 34.

Also, where you got the figure of 5-7 grand for batteries I don’t know. Supposedly the cost of a Prius complete replacement is $4,000 and needs replacing around the 7-8 year mark, but real costs seem to be more like $2,4000 or less. I’ve even heard of rebuilds costing no more than $500.

Ever checked on the cost to replace that tdi turbo? About $2,700. Then there’s VW’s famous “special tools”.

The biggest problems with the low rolling resistance tires, besides the inflated price, is how long they last. And that’s what isn’t very good. There are some new replacements like the hydroedge,that have almost as good mpg, but are guaranteed for 90,000 miles.

But they’re still basically twice the price of a standard tire. So you need to do the math, to see if it’s really worth the extra cost or not.

Van

To Mustang
Actually, the tires on my 2005 Ford Escape Hybrid have not only lasted 86,000 miles, and just now need replacement, but have performed incredibly even in snow and ice. I really have been amazed myself as I ski in the Northwest almost every weekend and have driven in all kinds of bad weather with them very happily.
I’m replacing the tires now and probably will stay with the Continental EcoPlus tires.

Tyres in Barnsley

It’s so interesting to see how you guys approach things in the USA. here in the UK we hve similar, yet different approaches.

Thanks for the information, it was very useful.

Stewart

dennis dickinson

rong tire psi then you where out the middle of the tire
i whent the other way because low rolling resistance rip off tires cost 325 each so i got regular ones @ 80 each.
my 4x civic with the same tires gets 31mph & now the Prius “with the same tires” gets 30
it’s simple math hybrids are a rip off

Qew

Hey dennis dickson,
Hybrids r a rip off? just got my 2011 honda insight,epa 40mpg city,43mpg highway.I got the lx,mid model,for just under 22 out the door.I drive 140 miles to work everyday,roundtrip,about 25 city and the rest highway,i have the cheapy stock dunlop tires everyone complains about and I’m getting just over 51 mpg avg. its not a straight away on the highway there are hills and drops.
Maybe you should recalculate your simple math..

LHO

Just returned from a 2,700 trip in a 2009 PRIUS. Higway travel consistantly 50 to 52 MPG. Inflation on original eqipment tires 36 psi. With over 50,000 miles, most are highway miles, this has been a pleasant and reliable experience. I keep accurate record of all road expenses, including, cost per gal, number of gallons, mipg. etc. Great to pass the pumps and save a few dollars at the same time.

LHO

Just returned from a 2,700 trip in a 2009 PRIUS. Higway travel consistantly 50 to 52 MPG. Inflation on original eqipment tires 36 psi. With over 50,000 miles, most are highway miles, this has been a pleasant and reliable experience. I keep accurate record of all road expenses, including, cost per gal, number of gallons, mipg. etc. Great to pass the pumps and save a few dollars at the same time.

ron vargo

Good discusion on tires. In order to save lots of money on fuel, ( I was driving a dodge durango that got 13.4 ave. gas milage) I bought a 2004 TDI Jetta 5 speed. I was considering the low resistance tires, but, now I dont think they are worth it for the extra price, and ride characteristics. I have been extremely happy with the jetta. 160,000 miles on it and I get 43 mpg city, and a whopping 62 highway only if I bump the speed down to 60mph. One tank of gas goes 600 miles easy for me. I call this farfromfullin.